Several of the major manufacturers of irrigation equipment, have spray heads with a pressure regulating valve incorporated into the sprinkler riser assembly. One such device is shown in U.S. Pat. No. 4,913,352. These devices all have “O” ring regulating piston seals which engage the inner surface of the riser tube to prevent leakage. Especially after they have been exposed to dirt and minerals in the water during use the friction between the seal and the tube can become quite high. To assure proper retraction of the piston, large powerful springs, e.g., exerting a force of 5-6 pounds, are required. To accommodate the large spring requires a large sprinkler head. As a consequence, there are no available pressure regulating nozzle assemblies that can be attached to the top of existing sprinkler assemblies. A need thus exists for a more compact pressure regulating nozzle assembly that can be easily attached to existing installed sprinkler risers to replace their existing non-pressure regulating nozzle assemblies.